Influence of hydrogenated diesel/H2O2 blend fuel on diesel engine performance and exhaust emission characterization

The oxygenated hydro diesel (OHD) is prepared from hydrogen peroxide (H2O2), acetone, and seaweed polysaccharide. A long-term study was carried out on the OHD fuel blend stability for about a year at various temperatures. The long-term stability shows very stable properties, no easy emulsion breaking, and a long storage period. The neat diesel and blend fuel performance test was conducted at various engine speeds, 1700–3100 RPM the diesel blend with 5 wt.% and 10 wt. % of H2O2 revealed the best fraction for reducing smoke and emissions. The blend contains 15 wt.% H2O2, revealing a significant reduction in exhaust temperature without considering the engine's performance. Moreover, the performance of the OHD also revealed an economizing rate, decreasing environmental pollution and prolonging the engine’s service life. The diesel engine performance and environmental evaluation leading to exhaust emissions characterization (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{CO}}_{\mathrm{X}}$$\end{document}COX, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{SO}}_{\mathrm{X}}, {\mathrm{NO}}_{\mathrm{X}}$$\end{document}SOX,NOX, and others). Based on the results, the various concentrations of H2O2 are an effective method for reducing the emission of diesel engines. Decreased CO, SO2, unburned hydrocarbons, and NO2 were also observed as percentages of H2O2. Due to increased oxygen content, water content and cetane number, the number of unburned hydrocarbons from diesel fuel decreased with the addition of H2O2. Therefore, the OHD blend can significantly curtail the exhaust emission of conventional diesel fuel, which will help reduce the harmful greenhouse gas emissions from diesel fuel sources.

www.nature.com/scientificreports/ The critical property of diesel fuel is its cetane number which affects ignition delay to combustion [13][14][15] . Fuel containing a higher cetane number enhances the combustion process during operation 16 . Yet, increasing concern over environmental protection and rigorous governmental regulations on exhaust emissions to reduce pollution has sparked a significant increase in engine development research 17 . Reducing particulate matter (PM) and NO X particularly in the Euro VI standards simultaneously is problematic owing to a converse relationship between NO X and PM 18 . Numerous researchers are dedicated to developing new or improved after-treatment technology to reduce NO X , PM and non-methane volatile organic compounds (NMVOC) emissions [19][20][21][22] . Selective Catalytic Reduction (SCR) is the most sophisticated active emissions control technology utilized effectively in diesel engine vehicles 23,24 . SCR uses a monolith catalyst to convert NOx into water (H 2 O) and diatomic nitrogen (N 2 ) 7 .
Due to sustainable development and environmental concern, substantial attention has been given to developing reformulated or alternative fuels. Many of these efforts have been focused on improving diesel fuel in the form of blended fuel to obtain durable and efficient superior blends to replace conventional diesel fuel. The primary diesel fuel blends developed thus far include ethanol [25][26][27][28][29] , biodiesel [30][31][32][33] , hydrogen 11,34,35 ; water-diesel 2,36,37 , vegetable oil [38][39][40] and various other oxygenated fuels [41][42][43][44] . It is widely thought that the reformulation of diesel fuels has played a significant role in attaining considerable reductions in exhaust emissions 39,[45][46][47] . The reformulation of diesel fuels brought additional advantages, including lowering sulfur and aromatic contents and the possibility of adding oxygen to the fuel. Many oxygenates-based additives have proven quite effective in reducing particulate emissions from diesel engines [48][49][50] . However, the most significant problem with diesel fuel is its reduced ability to dissolve other fuel blends. Once an additive is inserted as an adjunct, a sudden reduction in fuel properties is observed, especially in the number of cetanes drops significantly 51 . Diesel fuel partially mixes with ethanol, but solubility is affected due to the difference in surface tensions for both liquids.
Water is a typical diesel fuel additive that can be combined with diesel to co-existence an emulsifier 52 . Furthermore, water can be sprayed directly into the combustion chamber or fumigated into the intake air 53 . Recently, Atarod et al. 54 performed an experimental and modelling study on the nanoparticle-induced water-diesel emulsified fuel for emission control from the diesel engine. A mixture of Span 80 and Tween 80 was used for 5 wt.% while water content and nanoparticle composition varied between 0-3 wt.% and 0-150 μM, respectively. Findings revealed that adding water to a diesel fuel mitigated the unburned hydrocarbon emission and nanoparticle drops in the nitrogen oxide formation at moderate load conditions. Furthermore, the developed neuro-fuzzy-logicbased model effectively predicted the operating parameters and exhaust emissions from water-diesel blend fuel.
One of the best possible ways to introduce the oxygenate fuel is the insertion of H 2 O 2 in the diesel fuel blend, which has a higher cetane number tendency with additional water molecule [42][43][44] . However, previous studies illustrated that phase separation occurs with time by adding H 2 O 2 to an ethanol and diesel fuel solution 51 . Increased stability of the blend over a more extended period is also a significant issue 55 44 reported that increased H 2 O 2 enhances the cetane number of diesel fuel blends significantly. Moreover, these studies also revealed lower specific fuel consumption, particulate matter, smoke density, nitrogen oxides of nitrogen, carbon monoxide, and hydrocarbons compared to diesel fuel on its own or mixed with emulsified fuel 51 . Therefore, the present work focuses on studying the performance and emission characteristics of 5−15 wt.% added to diesel in the presence of a newly prepared polysaccharide polymer (agarose)/acetone emulsifier. In addition, the results are compared to the reference diesel (neat diesel). Our earlier study found the coherent stability of emulsified fuel. The experimental study also revealed that the increased H 2 O 2 contents in the diesel significantly enhanced the cetane number of fuel blends. Hence, the present work is a continuation of our previous study to investigate the influence of hydrogenated diesel/H 2 O 2 blend fuel on diesel engine performance and exhaust emission characterization, particularly in reducing NOx, CO, C x H y , and SO 2 .

Results and discussion
Comparison of comprehensive output energy at various speed. The output energy (OPE) at various speeds (rpm) is a tool for comparing the comprehensive performance of H 2 O 2 /diesel blend fuel with reference diesel (RD). Theoretically, it has measured how much fuel is being disbursed per breakup time to deliver maximum power. Figure 2 illustrates the generator output (kW) of the various test fuels at different engine speeds and various engine torque (6−12.5 Nm).
The results revealed that the RD fuel produced higher output at various engine speeds, almost 1-2.5%. However, emulsified H 2 O 2 /diesel blends showed lower output efficiency. The reason may be due to the relatively lower calorific value of H 2 O 2 /diesel fuel than the RD fuel discussed in our previous study 44 .
Amongst the H 2 O 2 /diesel blend fuel, the 5 wt.% of H 2 O 2 showed somewhat higher than higher H 2 O 2 /diesel blend content. Such negligible deficiency could be revealed due to their higher combustion efficiency and effective oxygen content in the diesel blend fuel, which is perhaps a good agreement for early combustion efficiency compared to RD diesel. Moreover, in our previous work 13,44,60 , we have already demonstrated that adding H 2 O 2 in the diesel enhanced the cetane number with thermal conductivity and specific heat. Perhaps the calorific value of the H 2 O 2 /diesel blend fuel scarcely lowered because of the lower energy contents of the fuel blends, despite all significances being agreeably within the scope of diesel fuel 47,61 . Specific fuel consumption (g/kWh). The current section of the study investigates engine performance using a convenient parameter of specific fuel consumption (SFC) and a comparison of the RD and H 2 O 2 /diesel blend fuel. The tests were conducted under various engine torque (6 12.5 Nm) and speed conditions ranging from 1700 to 3024 rpm. SFC indicates the ratio of fuel consumption rate to brake power output. Figure 3 summarizes the SFC of RD and diesel blend fuels; the results illustrated a decreasing trend as the engine speed increased from 1700 to 3024 rpm.
Because the test engine's fuel injection pump was of a customized type, the delivered fuel quantity decreased at the minimum default speed of Yanmar 62 , such as 1700 rpm. They simulated the breakup comparison rate www.nature.com/scientificreports/ regarding the RD fuel-air mixing rate and excess oxygen content within the diesel blend fuel. Increasing the engine speed improved system performance while decreasing the SFC of each test fuel. Nonetheless, the reduced volumetric coherence at higher speeds can reveal an SFC deficiency at speeds above 1700 rpm 62 . On average, the SFC of the RD test was higher than that of all H 2 O 2 /diesel blend fuels. RD fuel's SFC was 2-5% higher than H 2 O 2 /diesel. The test fuel contains 10 and 15 wt.% H 2 O 2 , respectively, and the diesel blend showed more promising SFC results than the diesel blend with 5 wt.% H 2 O 2 . H 2 O 2 demonstrated a 1.5 to nearly 5.2% reduction in SFC when compared to 5 wt.% H 2 O 2 /diesel and RD fuel, respectively. The higher SFC of the RD fuel than all H 2 O 2 /diesel blend fuels is attributed to the RD diesel's slightly higher energy scope. Technically, the heating values of the fuel blends were lower due to the molar volume contents of H 2 O 2 and emulsifier (C 14 H 24 O 9 /C 3 H 6 O); thus, consumption was supposed to be increased to achieve slightly more than 11 Nm torque. Despite having relatively lower heating values, all H 2 O 2 /diesel blend fuels had lower SFC than RD fuel. The reason for effective SFC is due to the higher cetane value of the H 2 O 2 /diesel fuel blend 51 . When the cetane number of blend fuel rises with increased quantities of H 2 O 2 , the temperature and oxygen content in the combustion chamber are in more self-control, promoting thermal cracking and increasing oxidation rates while decreasing unburned HC emissions and specific fuel consumption 63 . It also suggests that adequate SFC of the H 2 O 2 /diesel blends is perhaps found because of the presence of stable high oxygen contents in the diesel blend.
Smoke density (SD). The exhaust smoke density, also called multiple particulate matter (PM), relates to unburnt hydrocarbons (H x Y x ), NO x , and SO x and has proven to be a critical issue for diesel fuel. Therefore, since the last decay, developed countries have made rigorous policies to restrict light-grade diesel (EURO II and III) usage in public automobiles. Yet the PM, particularly H x Y x and NO x , are still challenging in European countries due to the freezing environment 10,12 . Even though public transport uses high-speed diesel (EURO V and VI) followed by advanced technology like in-cylinder and advanced hybrid oxidation catalysts with catalytic filters system.
Thus, this section investigated a comprehensive assessment of the engine performance on the SD of different H 2 O 2 /diesel blend fuels. The SD analysis was carried out using an AVL smoke meter during the test running condition with variable torque (6−12.5 nm) followed by different engine speeds ranging from ~ 1700 to 3600 rpm. The SD results can be seen in Fig. 4; the SD comparison of H 2 O 2 /diesel blends with RD fuel showed a decreasing tendency as the engine speed increased from 1700 to 3600 rpm.
It has also been noticed that the SD followed a similar trend level to Fig. 4 decreases for each H 2 O 2 /diesel blend than the RD. However, the drought of SD showed a significant drop in all H 2 O 2 /diesel blend fuel, about 10-25% reductions. The reduction of SD level was probably revealed due to excess oxygen content, which has also been attributed to better mixing of intake air and fuel and an increase in the OH radical molar mass contents in the combustion chamber 38,51,64 . Usually, the components of diesel fuel exhibit an intense interaction capability with oxygen. Furthermore, the stability of diesel/H 2 O 2 is higher, secondary combustion is reduced, and combustion performance is enhanced.
Moreover, our previous studies have demonstrated that the emulsifier used in H 2 O 2 and diesel prevented the phase rift between diesel and H 2 O 2 , as seen in Fig. 4 44 . Therefore, H 2 O 2 likely invariably reduces soot and PM emissions in diesel. Also, it could be the consequence of rapid fuel breaking up due to the distinct engagement of oxygen content in the fuel combustion chamber, probably more related to smoke density. The highest SD reduction was obtained by 15 wt. of H 2 O 2 diesel blend fuel at maximum load conditions is 26% (see Fig. 5). www.nature.com/scientificreports/ Also, Fig. 5 shows the lower peak value attained by the 5 wt.% of H 2 O 2 in the diesel blend fuel at a load speed of 2900 rpm is about 12%. The smoke density is further decreased with the 10 wt.% H 2 O 2 addition in diesel blend because of excess oxygen content. Thus, it presumably revealed the molar volume difference between the agar/acetone (C 14 H 24 O 9 /C 3 H 6 O) and the H 2 O 2 added diesel blend fuel, which might reveal the direct relevancy of SD and particulate matters (H x Y x + No x ) to each other. Particulate reduction will most likely be due to a good agreement in the combination of acetone and H2O2 in diesel fuel, which may act as an oxidizing agent to keep the combustion chamber clean. In addition, the SD is reduced for the H 2 O 2 /diesel blends because of the higher molar mass contents of hydrogen in the emulsifier. Thus, it can also be combusted practically as SD-free under a specific combustion environment 65 Figure 6a and b summarize the emission results of CO and CO 2 from loaded and unloaded generator exhaust, respectively. The test results (see Fig. 6a and b) of the unloaded engine revealed reference diesel (RD) CO emissions of 565 ppm and 706.25 ppm loaded, compared to 437.5 ppm and 525.4 ppm (loaded). It is generally known that diesel fuel requires more oxygen to be burned, so in the case of a fully loaded diesel engine, combustion requires a greater amount of air intake to be drowned out by each intake stroke, regardless of the position of the throttle. The air is then compressed and heated before diesel fuel is fed into the cylinder. When fuel is exposed to a higher amount of hot air, it rapidly burns. This results in a higher concentration of COx and NOx exhaust gases in the loaded engine compared to the unloaded engine. The three best diesel/H 2 O 2 blend emulsions were evaluated in order to reduce CO content.
The UL generator shows that the 5 wt.% of H 2 O 2 in the diesel blend represents a 22.5-25% reduction. The 10 wt.% of the diesel blend reduced CO emissions to 348.5 ppm, a 38% reduction, and the 34.8% reduction of CO emissions represents the 15 wt.% of H 2 O 2 in the diesel blend. The 10 wt.% of H 2 O 2 in the diesel blend shows the greatest reduction in CO emissions of the UL generator. Theoretically, the air/fuel equality ratio is defined as the difference between the definite air/fuel ratio and the stoichiometric air/diesel ratio in the compression chamber of a diesel engine 58 . In contrast, in the case of H 2 O 2 /diesel, the unstable peroxide likely provides some of the oxygen needed for the diesel to be ignited early, reducing the need for additional air in the compression chamber. Technically speaking, if the required amount of oxygen is present, then the UL diesel engines run on the leaner side of stoichiometry, CO emissions are very low in the case of an additional molar volume of peroxide in the compression chamber.
However, the loaded generator has CO emissions of about 400.7 ppm, which is 13% higher than the unloaded generator but smaller than the loaded and unloaded generators of RD fuel. It is suggested that in the case of a fully loaded diesel engine, the diesel requires more oxygen, and the probably unstable oxygen present in the diesel emulsion is probably not enough for the ignition. Therefore, the compression chamber takes in more air, and thus the contents of the CO emissions are higher than in the UL-loaded diesel engine. Nevertheless, the 15 wt.% of the diesel blends also show lower CO contents in the loaded and unloaded generator than the reference diesel but are a little higher than the 5 and 10 wt.% of the diesel blend composition, respectively. www.nature.com/scientificreports/ Nevertheless, the loaded generators show almost 10-20% higher emissions than the unloaded generator in all the fuel tests. The loaded generator required more power and more fuel and air intake to be combusted, thus consequently higher the rate of CO emission. It is probably because the higher molar mass of oxygen in the diesel blend composition and higher contents of CO in the reference diesel emissions are in good agreement due to the air intake inside in-cylinder combustion. Moreover, the tendency H 2 O 2 is entirely reactive, flaring once it has ideal environments like ignition in a closed chamber. Thus, it reacts independently and does not need any oxidizer, helping the diesel for an early and clean combustion process. But the higher amount of H 2 O 2 in the blend yet contributes to reducing the contents of CO. Gribi et al. 67 also found that H 2 O 2 has individual combustion characteristics. They have reported that H 2 O 2 can be used as a fuel or an oxidizer when reacting with other fuels, particularly in combustion chambers. Thus, it assumes the dual nature of H 2 O 2 and explores its potential benefits in clean combustion technology. Figure 6c and d also shows the H 2 O 2 impact on reducing CO 2 parts of the unloaded and loaded diesel generator's exhaust stream. Although reference diesel had a very low CO 2 emission (1.2%), the 5% H 2 O 2 fuel  www.nature.com/scientificreports/ blend slightly increased the CO 2 emission to 1.75%. Similar results are also observed in loaded generators, and the CO 2 emission exhibits higher content but is lower than the RD diesel emission, either loaded or unloaded generator. However, the values of CO 2 emissions for higher percentages are quite like RD (1.2%), and the effect is not significantly evident on CO 2 emission. Al-lwayzy et al. 69 and Scragg et al. 70  The primary mechanism causing the reduction in exhaust emissions looks like the decrease in the temperature of the combustion products as a result of vaporization of the liquid water and subsequent dilution of the gas-phase species. NOx results found positive impacts on concentrations of NO 2 and nitrous oxide (NO) in the diesel fuel exhaust streams, either unloaded or loaded generators. Figure 8 illustrates an overall reduction comparison in www.nature.com/scientificreports/ nitrogen dioxide and nitrous oxide emissions due to the solid oxidizing capacity of H 2 O 2 as it decomposes in the combustion chamber to oxygen and water. Water produced during this reaction absorbed heat which, in turn, slightly decreased the temperature in the combustion chamber. This reduction in a temperature limited the production of NO 2 and NO. Although reference diesel has very low emissions of NOx (12 ppm), the 5 and 10 wt.% of H 2 O 2 in the diesel blend decreased its formation to 9 and 5.8 ppm, respectively. The reduction of NO x formation caused by the combination of higher cetane number and water content reduces the diesel engine's temperature 13,43,51 . Similar results are also observed in loaded generator emissions. The significant reduction of nitrogen-based emissions of blend fuel on unloaded or loaded generators might be a possibility of rapid vaporization and disassociation of H 2 O 2 into hydroxyl radicles. In addition, it can also be interpreted that the H 2 O 2 has become strenuously unstable and highly active in the combustion chamber, consequently oxidizing the NO and NO 2 in the exhaust. Kasper et al. 68 also investigated the significance of H 2 O 2 on the decomposition and reduction of nitrogen-based emissions; they have experimentally demonstrated that NOx can be oxidized to NO and NO 2 in the gas phase by OH radicals generated by the thermal decomposition of H 2 O 2 . Similar results were also observed by Saravanan et al. 72 . and Ashok & Saravanan 51 , in their studies of H 2 O 2 -diesel blends, found an overall reduction of about 18.5%. Figure 8 also shows the results of Nox, and it was noticed the, the 5 wt.% of H 2 O 2 in the diesel blend shows higher NOx contents in UL and FL generater emission. It has been found that a 5% H 2 O 2 diesel blend doesn't make a big difference in reducing NOx and CO 2 . This is likely because there isn't as much H 2 O 2 in the diesel, but it does produce less heat (see Fig. 10) than RD diesel, regardless of whether the UL or FL generator. Although the temperature reduction is 2-20% in the case of 5% H 2 O 2 /diesel blend fuel exhaust, this gap is probably not enough to overcome the reduction of NOx and CO 2 . On the other hand, higher the concentrations (10-15%) of H 2 O 2 in the diesel blend shows significant reduction in the NOx in UL and FL generator emissions. It seems that a higher water content level in the diesel blend reduces the temperature of the combustion chamber, resulting in a lower NOx concentration.
Typically, the combustion temperature, oxygen concentration, and the retention time of the combustion product in the combustion zone are often the most prevalent variables determining the amount of NOx generated. The high temperature inside the cylinder caused by the high compression ratio encourages NOx emission, and the RD results show good agreement with the experimental results 74 . The local adiabatic flame temperature is reduced by the heat of vaporization and sensible heating of water, which also reduces NOx generation. Therefore, the higher the concentration of H 2 O 2 in the diesel blend, the greater the reduction in NOx 75 . Scrage 70 and Koc 71 reported similar results, which increased the water and oxygen contents while decreasing NOx and CO 2 , but the CO 2 reduction is not yet significant. Perhaps it might be overcome in the case of the alteration of the engine.
Hydrocarbon emissions from diesel engine exhaust are also essential pollutants. The H 2 O 2 /diesel blends also demonstrated constructive impacts on the total hydrocarbon content of the diesel generator's exhaust stream. Figure 9 shows comparisons of the overall reduction in the concentration of unburned hydrocarbons (CxHy) due to the considerable oxidizing property of H 2 O 2 .
The RD fuel shows higher CxHy content emissions in unloaded and loaded generator exhaust. The diesel blend fuel has a 5wt.% of H 2 O 2 /diesel blend and didn't reveal CxHy content in the unloaded and loaded generator exhaust. However, the 10 wt.% of H 2 O 2 in the diesel blend slightly increased the production of unburned hydrocarbons. The 15% H 2 O 2 in the blend is lower than RD diesel and the 10 wt.% H 2 O 2 /diesel blend. The lower level of unburned hydrcarbons is most likely due to the formation of acetone peroxide prior to the solution being www.nature.com/scientificreports/ mixed with the diesel. which most likely acts as a strong oxidizing reagent in the combustion chamber, and once diesel is ignited, this acts as a cleaning tool along with water vapors to overcome the unburned hydrocarbon reduction in the higher concentration of H 2 O 2 in the diesel blend. Moreover, the results revealed that, as the concentration of H 2 O 2 in the blends increased, unstable oxygen contents improved due to the peroxiding nature of H 2 O 2 , although viscosity, density, and high heat value decreased slightly 47,73 . In general, higher density and lower viscosity lead to higher flow; thus, these findings suggested that the lower viscosity of diesel/H 2 O 2 blend fuel could succeed in lowering fuel injection with an early ignition time 47,73 , which could result in a good agreement in the reduction of unburned hydrocarbons and NO x . Furthermore, the higher molar ratio of the peroxide group resulted in a drop in the viscosity of each stable blend compared to RD and a lower concentration of H 2 O 2 in fuel blends. It also suggested that the 70% water content of H 2 O 2 formed water droplets inside the diesel, and these droplets mixed well due to the polysaccharide polymer in the H 2 O 2 /diesel blend.
Nevertheless, unburned hydrocarbon emissions were well below those from pure diesel fuel. In terms of particulate matter (PM) emissions, the presence of water during the intensive formation of soot particles appears to significantly reduce and enhance burnout by increasing the concentration of oxidation species such as OH 73 . Figure 10 compares the exhaust temperature of the unloaded and loaded generator at maximum power output. The exhaust temperature of RD fuel shows a higher temperature than all H 2 O 2 /diesel blend fuels either the generator is unloaded r or loaded at maximum power output. The higher exhaust temperature of RD fuel was revealed due to the higher heat of evaporation and delayed combustion process of lean diesel. However, all H 2 O 2 /diesel blend shows almost 20-41% lower exhaust temperature of the loaded generator.
Due to the higher cetane number H 2 O 2 , it has a lower latent heat of evaporation than diesel. The ignition delay for H 2 O 2 /diesel fuel diminishes, resulting in a low exhaust temperature 13,44,72 . In addition, during typical engine running, the coolant absorbs the majority of the heat. The H 2 O 2 also has water particles, which interact with the coolant and absorb more heat, decreasing or controlling the exhaust emission temperatures 51 . The peak engine temperature constantly boosts NOx generation. Including H 2 O 2 in the diesel blend raises the cetane rating, which precedes a reduction in ignition latency. This decreased ignition delay reduces the amount of fuel accumulated before to combustion and lowers the initial combustion rates, lowering the peak temperature and thus lowering NOx generation. Reducing NOx, COx, and CxHy in exhaust emission is a significant agreement to justify the temperature reduction 60,73 . Figure 10 also compares air intake amounts during the combustion process. Compared to RD diesel, the H 2 O 2 /diesel blend fuel shows lesser air intake in the combustion process, probably due to the availability of required oxygen in the combustion chamber. Preparation of emulsifier and diesel/ H 2 O 2 fuel blend. The emulsifier was prepared before mixing reference diesel (RD) and H 2 O 2 diesel fuel blend. A polysaccharide polymer (PSP) and acetone reaction at a ratio of 1:4 w/v were accomplished in a 500-mL sealed Schott bottle. A heated magnetic stirrer mixed the solution at 50 C for 12 h. The diesel/H 2 O 2 fuel blends were prepared with a customized solvent condensation apparatus described elsewhere 13,44,47 . During the preparation of diesel/H 2 O 2 fuel blends, the amount of PSP emulsifier was kept at 5 vol %, and the volume ratios of H 2 O 2 to RD varied in the range of 5-15 wt.%. Mixing the PSP emulsifier and H 2 O 2 took 30 min to form a stable homogenized solution. As a final point, 91% of RD was inserted into the mixing vessel and kept during the mixing process until 70 min. A well-stabilized emulsion is formed utilizing the hydrophobic, hydrophilic, and lipophilic nature of the PSP emulsifier and by the sharing effects produced by the high-speed fluid stirrer in the vessel with emulsified fuel blend. All the fuel blend formulations were carried out at a constant speed of 100 rpm under variable loading conditions and kept the temperature of the fuel blend preparation at the ambient temperature of 25 ± 1 °C.

Experimental setup and procedure of engine test trial for diesel blend fuel. A Yanmar L48
N single-cylinder, four-stroke, direct-injection diesel engine with an output of 3.6 kW (4.7 ps) and a variable speedometer controller 53 , typically used for agricultural and residential electricity production, was the subject of the current investigation. The detailed specifications of the diesel generator are compiled in Table 1. The singlecylinder engine was chosen because it was compact and simple to maintain. The system is more suited for hot and arid circumstances because it is air-cooled, so there is no need for a radiator, water body, or pump. The test engine (a diesel generator) is shown in Fig. 11 and has been modified with four Philips 32150-5 1000 W highintensity discharge lamps to investigate the engine load test. The load on the generator was measured using a Digital Generator Current Voltage Power Energy Meter (QV05 MK 11-380; S/N 36220526). Every measurement is taken and manually recorded. Run the engine for roughly 10 min on reference diesel fuel before starting it. The fuel flow rate was calculated using a calibrated burette and a digital stopwatch. Figure 11 displays the schematic diagram of the experimental setup together with all of the instrumentation. Before each experiment, the emission analyzer was zeroed out and calibrated for a conventional diesel engine.
Exhaust emission analysis on diesel generator. As discussed earlier, exhaust emissions are one of the most significant problems associated with diesel fuel and thoughtfully contribute to environmental pollution. The major components of nearly all gas combustion products are N 2 , CO 2 , CO, and water vapour. They are not poisonous or toxic, although carbon dioxide has generally been recognized as a critical greenhouse gas con- www.nature.com/scientificreports/ 4 analyzer satisfies the standards of the US EPA CTM 034 reference method, with a maximum detection limit variation of 2 ppm for exhaust gases and unburned hydrocarbons from 0.1 ppm. The probe of the analyzer was inserted with the exhaust stream outlet of the diesel generator to determine the amounts of the pollutants such as carbon-based emissions (CO from high range to compensated and CO 2 ), nitrogen-based emissions (NO, NO 2 , NOx-calculated where NO 2 the sensor was not fitted), SO 2 , H 2 S , Hydrocarbons ( C x H y ), respectively.

Conclusion
In this experimental study, specific effects from the addition of hydrogen peroxide (H 2 O 2 ) to diesel fuel were systematically observed for various compositions of fuel blends to discover an optimal blend that best enhances the performance of diesel fuel exhaust emissions. Due to the environmentally friendly nature of H 2 O 2 , improved ambient effects on unloaded and loaded diesel generator emissions were robustly determined and demonstrated by this study. Reduced emissions of CO, SO 2 , and unburned hydrocarbons along with NOx were achieved as the H 2 O 2 content of the fuel blend was slightly increased. The study also demonstrated that while the addition of 5 wt.% H 2 O 2 slightly increased the concentration of CO 2 , the amount of CO was reduced to about 25.6% for full load conditions. The number of unburned hydrocarbons (CxHy) from enhanced combustion decreased due to increased oxygen content during the combustion process. Overall, the superior environmental properties of the H 2 O 2 /diesel fuel blend were perhaps observed due to the higher cetane number potential of H 2 O 2, water content and adequate oxygen, which provide complete combustion with a slightly reduced temperature profile. Resulting in form of complete combustion with reduced acidic gas formations (Cox, SOx and NOx). Thus, this experimental study demonstrated that 5 and 10 wt.% of H 2 O 2 in diesel blend fuels could be best suggested after physicochemical, thermal, and exhaust emission characterization. Therefore, this study will make an effort to contribute to the ongoing research for greener diesel fuel and to curtail the harmful greenhouse impact of conventional diesel fuel, which can contribute to reducing carbon and greenhouse emission goals.

Data availability
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.